RFI issues in the Ford Explorer by pengtt


									                     RFI issues in the Ford Explorer
                                  and My 2002 Sport Trac

                                    by Pat Freeman, N3GWZ
                                         April 30, 2002

I’m a ham radio operator who enjoys using HF, VHF and UHF frequencies to communicate with
other ham radio operators around the world while driving. Prior to purchasing my 2002 Explorer
Sport Trac (ST), I logged many interesting conversations including US to Europe/Asia contacts
using as low as 1 watt of power in Single Side Band mode! However, my ST was emitting a lot of
Radio Frequency Interference preventing me from hearing most signals. In this Tech Tip, I hope
to provide a unique way to fix Ford’s problem. This article should be beneficial to CB operators
as well.

I first began noticing that my ham radio showed an S8 buzzing / whining noise in almost every
mode, USB, LSB, AM, FM, etc. I talked with other hams that suggested building a “sniffer” in
order to pinpoint where the noise is coming from. I connected a piece of coaxial cable to my ham
radio with a small wire antenna at the other end and proceeded to walk around my ST while it
was running, watching the S meter. At the fuel tank, the S meter showed the S8 level. Other
trouble areas were under the hood and near the exhaust, but these were only S4 and lower
levels. I found my culprit at the fuel tank.

Further investigation on the Internet resulted in learning that Ford had issued a Technical Service
Bulletin (TSB) which informed their service departments that the fuel pump, located inside the fuel
tank, was causing problems on select Ford vehicles up to 1999. TSB #9117-5 referenced
installing a Filter Kit, Ford Part # E7PZ9B357A, on the power leads of the fuel pump. However,
my dealer would not install this kit because the TSB was old. Another dealer ended up installing
a different kit as per TSB #01-7-3, part #F1PZ18B925A under warranty. My ham radio had the
same noises, however, so I had to come up with a fix of my own. Other hams suggested
purchasing toroid cores and wrapping several turns of the power leads through the core. An
article on the Internet referenced using type 2 toroid cores that contained a material capable of
suppressing frequencies in the 2MHz to 30MHz area. However, after testing this idea, these
toroids weren’t enough to stop the noise.

I finally decided to fabricate my own RFI filter by purchasing 4 of Radio Shack’s Snap-on RF
Chokes, part #273-105. These chokes are square and made of a toroid material. They open in
the middle to allow you to wrap several turns of wire through them. I also needed to pick up
additional wire if I intended to wrap more than one turn through the choke. I picked up the
red/black 18 gauge wire and some quick-disconnect butt connectors also. I wrapped the 18
gauge wire around a few chokes and installed on the power leads on my ST. My power leads
were pink and black and were easily accessible when I lowered the spare tire out of the way.
Check a wiring diagram or probe the wires on your Explorer with a volt meter to see which leads
are correct. As shown in the pictures below, I cut the power leads using wire cutters and installed
the butt connectors inline using a crimp-tool. This allowed me to install the homebrew RFI filter
and test it. If it didn’t work, I could reconnect the fuel pump power leads and forget about using
the ham radio.
                                                                        Looking at the fuel tank.

The fuel pump power leads.

I started with two chokes and ultimately had to wire four chokes together in order to suppress all
of the RFI being generated by the fuel pump on the power leads. I also included three T-50-2
toroids (little red “beads”) but you should be able to get satisfactory results from the chokes. I
wrapped the 18 gauge wire through the chokes 7 times to create a large amount of inductance
and “trap” the RFI between this filter and the fuel pump. Butt connectors were installed on the
leads of this assembly using a crimp-tool.
                                                                           The filter assembly.

I installed the choke assembly inline using the butt connectors I crimped to the power leads and
tested the results.

             Filter installed.
I was happy with the results so I sealed the butt connectors with 3M Splicing Tape. You may
want to inject some dielectric grease, available at most auto stores, into the butt connectors to
prevent corrosion. I then wrapped the wires in electrical tape and zip-tied the assembly to an
existing hose.

                                                                  Filter assembly completed.

I hope that this Tech Tip helps you resolve the RFI issues you might be having in your Explorer!

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